Base-station cell design method and base-station cell design apparatus, and program thereof in mobile communication system

ABSTRACT

The above base-station cell design method is for sequentially adding base stations, and a technique of which throughput is few is employed for a radio-wave propagation characteristic evaluation to be made in this addition, and a technique of which the throughput is much, but which is of high-precision, more specifically, a technique such as the ray tracing is applied for the radio-wave propagation characteristic evaluation to be made after addition. The result of the high-precision radio-wave propagation characteristic evaluation to be made after this addition is put to practical use for estimating an interference quantity in selecting the arrangement location of the base station to be added newly. This allows the quantity of the radio wave analytic processing, which accounts for a large majority of the base-station cell design processing, to be reduced, thus enabling a fast base-station cell design.

BACKGROUND OF THE INVENTION

The present invention relates to a base-station cell design method, anapparatus and a program thereof in a radio communication system, andmore particular to a base-station cell design technique such asbase-station layout and base-station parameter setting in a mobilecommunication system.

A conventional base-station cell design technique will be explained byuse of FIG. 17. Base-station candidates are arranged in locationsdisplayed with black squares A02 to A06 on a service area A11 toevaluate a rate of areas A01, and A07 to A10 to be covered by the abovebase-station candidate group to a service area A11, i.e. an areacoverage ratio. Similarly, the area coverage ratio is evaluated for theother arrangement location as well to repeat its evaluation until abase-station arrangement pattern in which a desired area coverage ratiois reached is obtained. In the event of making base-station installmentof a trial-and-error optimal-arrangement search type like this, adetailed evaluation of a radio-wave propagation characteristic extendingover the entire service area is required base station by base stationwhenever the base-station arrangement is given.

As another technique, there is a technique that a human beingpre-narrows down a pattern to be evaluated for realizing a reduction inthe computation time (for example, a patent document 1). Also, as yetanother technique, there is a technique of employing genetic algorithmfor realizing a reduction in the time required for theoptimal-arrangement research (for example, a patent document 2). Afurther additional technique will be explained by employing FIG. 18 (forexample, a non-patent document 1). In this non-patent document 1 wasdisclosed a base-station cell design technique of pre-arranging theregularly placed base stations in the locations indicated with blacksmall points B02 within a service area B01 to sequentially delete thebase stations that did not contribute to an increase in a covered area.It is required to make a high-precision radio-wave analysis within allthe service area for all base-station candidates pre-arranged regularly.

[PATENT DOCUMENT 1]

JP-P1996-317458A (page 2 to 3, FIG. 1 to FIG. 3)

[PATENT DOCUMENT 2]

JP-P2001-285923A (page 2, FIG. 1)

[PATENT DOCUMENT 3]

JP-P2002-107397A

[NON-PATENT DOCUMENT 1]

M. Kamenetsky, et. al. “Coverage Planning for Outdoor Wireless LANSystem”, 2002 International Zurich Seminar on Broadband CommunicationAccess, Transmission, Networking, February 2002, pp49-1 to 49-6

[NON-PATENT DOCUMENT 2]

Proc. of International Symposium on Antennas and Propagation Society,1991, vol. 3, pp. 1540-1543

It has been generalized that the base-station cell design in a cellularsystem employs a specialized tool; however a covered area of an accesspoint (AP: equivalent to the base station) is extremely narrow, a simplepropagation-loss estimation equation employed in a conventional cellularsystem design is impossible to apply in a wireless LAN system to beinstalled in the environment where a lot of propagation disturbingobjects such as a building exist in a line-of-sight propagation area ofa radio wave, and a detailed radio-wave analysis, which took amicroscopic structure such as a geographical feature of a target areaand the building into consideration, is required.

A ray tracing technique is commonly used as a technique of thehigh-precision radio-wave analysis; however upon employing the celldesign technique of the trial-and-error optimal-arrangement search typeas shown in FIG. 17, as the case may be, there is the possibility thatit takes an unrealistic processing time to gain a solution because theabove technique needs a lot of computations. Needless to say, bynarrowing the service area to be taken as an object of design, the APnumber that has to be arranged is reduced, which enables a reduction inthe processing time; however the base station number to be arranged perarea becomes extremely numerous in a picocell environment like thewireless LAN, as compared with a macrocell/microcell environment in theconventional mobile communication system, whereby the problem occursthat the size of the area that can be designed within the realisticprocessing time does not come up to the necessary size of the area byfar.

In other words, in designing the picocell system, a difficult task hasto be tackled of coping with an increase in a base-station layoutdensity while a radio-wave analysis, which requires a lot of thecomputations and is of high precision, is employed, that is, it isindispensable to achieve the fast base-station cell design algorithm.

Upon employing the base-station cell design technique disclosed in thepatent document 1, the computation time can be reduced because a humanbeing pre-narrows down the location candidates. However, the resultvaries anyway, depending upon the AP layout candidate selected firstly,and vague elements such as a perception and an experience of a designerdictate the selection of the AP layout candidate, thus the problemexisted that an appropriate cell design was not always possible toguarantee.

The vagueness of the perception/experience of the designer can beexcluded in the base-station cell design technique disclosed in thepatent document 2; however it was pointed out that the solution did notconverge, depending upon pre-setting of parameters such as initiallayout, which gave rise to occurrence of an unstable phenomenon such asdivergence and oscillation, and the problem existed that if there rosethe situation where the convergence of the solution was unpromising, awork had to be done over again from the beginning.

In the base-station cell design technique disclosed in the non-patentdocument 1, there is no vague element like one shown in the patentdocument 1 at the time of the design, and also, such an unstablephenomenon shown in the patent document 2 does not occur. However, thebase station number to be pre-determined, which is required for makingan effective cell-layout design, is more than several tens of times aslarge as the base-station number to be determined finally. Thus, whenthe radio-wave analysis is made in terms of the plane in details withinthe service area with all candidate points thereof taken as atransmission point, after all is said and down, the enormous computationtime is necessitated.

Also, either of the above-mentioned prior arts, which are for aimingonly for optimization of the layout of AP, have no setting method ofvarious design parameters (a transmitted electric power, channelallocation, etc.) shown. Also, in the event of making wide-rangedevelopment a plurality of the stations, an offset of the trafficdensity that depended upon the location becomes noticeable; however notraffic density was reflected in the cell design in either of theabove-mentioned prior arts.

SUMMARY OF THE INVENTION

The present invention relates to a base-station cell design method of,in a case where the service area that becomes an target, and a trafficdensity distribution were given, arranging a plurality of the basestations to cover the above service area, and an objective thereof is toprovide the base-station cell design method, and the apparatus and theprogram thereof that enable the arrangement of the base stationsatisfying a desired traffic coverage ratio (a rate of the traffic to beabsorbed by the installed base station to all the traffic within thetarget service area), and the setting of the parameters (specifically,the channel allocation and the transmitted power), on the premise that adetailed radio-wave analysis simulator such as the ray tracing is put topractical use.

Another objective of the present invention is to provide thebase-station cell design method, and the apparatus and the programthereof that enable exclusion of the vagueness without a necessity forthe perception and experience of a person in selecting the base-stationlocation candidate.

Yet another objective of the present invention is to provide thebase-station cell design method, and the apparatus and the programthereof that enable a fast base-station cell design by reducing thequantity of the radio-wave analytic processing that accounts for a greatmajority of the base-station cell design processing.

The base-station cell design method in accordance with the presentinvention, which is a base-station cell design method adapted so that,in designing a base-station installment in a mobile communicationsystem, a plurality of base-station candidate locations are given withina service area to install a base station in anyone of these base-stationcandidate locations, is characterized in including: anobjective-function calculation step of calculating a predeterminedobjective-function responding to a traffic absorption quantity and (or)a communication quality value in each of said base-station candidatelocations; and a base-station layout decision step of deciding a layoutat which the base station is installed responding to thisobjective-function.

Another base-station cell design method in accordance with the presentinvention, which is a base-station cell design method adapted so that,in designing a base-station installment in a mobile communicationsystem, a plurality of base-station candidate locations are given withina service area to decide anyone of these base-station candidatelocations as a base-station installment layout while a radio-wavepropagation characteristic estimation technique is used, ischaracterized in including the steps of: as a radio-wave propagationcharacteristic estimation technique within said service area with eachof said base-station candidate locations taken as a transmission point,using a first radio-wave propagation characteristic estimation techniquehaving a first precision to additionally install said base station; andas a radio-wave propagation characteristic estimation technique withinsaid service area with a base-station additional-installment locationafter a case where said based station was installed taken as atransmission point, using a second radio-wave propagation characteristicestimation technique having a precision higher than said firstprecision.

Yet another base-station cell design method in accordance with thepresent invention, which is a base-station cell design method in amobile communication system, wherein a service area, and a trafficdensity distribution within this service area are given to arrange abase station in the above service area, is characterized in including abase-station layout decision step of, with a rate of a total trafficquantity that can be absorbed by the base stations arranged within saidservice area to all the traffic quantity that occurs within said servicearea taken as a traffic coverage ratio, sequentially deciding layouts atwhich the base station is installed until said traffic coverage ratioexceeds a desired traffic coverage ratio.

The base-station cell design apparatus in accordance with the presentinvention, which is a base-station cell design apparatus adapted sothat, in designing a base-station installment in a mobile communicationsystem, a plurality of base-station candidate locations are given withina service area to install a base station in anyone of these base-stationcandidate locations, is characterized in including: objective-functioncalculation means for calculating a predetermined objective-functionresponding to a traffic absorption quantity and (or) a communicationquality value in each of said base-station candidate locations; andbase-station layout decision means for deciding a base-station layout atwhich the base station is installed responding to thisobjective-function.

Another base-station cell design apparatus in accordance with thepresent invention, which is a base-station cell design apparatus adaptedso that, in designing a base-station installment in a mobilecommunication system, a plurality of base-station candidate locationsare given within a service area to decide anyone of these base-stationcandidate locations as a base-station installment layout while aradio-wave propagation characteristic estimation technique is used, ischaracterized in including the means for: as a radio-wave propagationcharacteristic estimation technique within said service area with eachof said base-station candidate locations taken as a transmission point,using a first radio-wave propagation characteristic estimation techniquehaving a first precision to install said base station; and as aradio-wave propagation characteristic estimation technique within saidservice area with a base-station installment location after a case wheresaid base station was installed taken as a transmission point, using asecond radio-wave propagation characteristic estimation technique havinga precision higher than said first precision.

Yet another base-station cell design apparatus in accordance with thepresent invention, which is a base-station cell design apparatus in amobile communication system, wherein a service area, and a trafficdensity distribution within this service area are given to arrange abase station in the above service area, is characterized in includingbase-station layout decision means for, with a rate of a total trafficquantity that can be absorbed by the base stations arranged within saidservice area to all the traffic quantity that occurs within said servicearea taken as a traffic coverage ratio, sequentially deciding layouts atwhich the base station is installed until said traffic coverage ratioexceeds a desired traffic coverage ratio.

The program in accordance with the present invention, which is a programfor causing a computer to execute a base-station cell design methodadapted so that, in designing a base-station installment in a mobilecommunication system, a plurality of base-station candidate locationsare given within a service area to install a base station in anyone ofthese base-station candidate locations, is characterized in including:an objective-function calculation step of calculating a predeterminedobjective-function responding to a traffic absorption quantity and (or)a communication quality value in each of said base-station candidatelocations; and

a base-station installment step of deciding a layout at which the basestation is installed responding to this objective-function.

Another program in accordance with the present invention, which is aprogram for causing a computer to execute a base-station cell designmethod adapted so that, in designing a base-station installment in amobile communication system, a plurality of base-station candidatelocations are given within a service area to decide anyone of thesebase-station candidate locations as a base-station installment layoutwhile a radio-wave propagation characteristic estimation technique isused, is characterized in including the steps of: as a radio-wavepropagation characteristic estimation technique within said service areawith each of said base-station candidate locations taken as atransmission point, using a first radio-wave propagation characteristicestimation technique having a first precision to additionally installsaid base station; and as a radio-wave propagation characteristicestimation technique within said service area with said base-stationadditional-installment location after a case where said base station wasinstalled taken as a transmission point, using a second radio-wavepropagation characteristic estimation technique having a precisionhigher than said first precision.

Yet another program in accordance with the present invention, which is aprogram for causing a computer to execute a base-station cell designmethod in a mobile communication system, wherein a service area and atraffic density distribution within this service area are given toarrange a base station in the above service area, is characterized inincluding a base-station layout decision step of, with a rate of a totaltraffic quantity that can be absorbed by the base stations arrangedwithin said service area to all the traffic quantity that occurs withinsaid service area taken as a traffic coverage ratio, sequentiallydeciding layouts at which the base station is installed until saidtraffic coverage ratio exceeds a desired traffic coverage ratio.

Another base-station cell design method in accordance with the presentinvention, which is a base-station cell design method of, in designing abase-station installment in a mobile communication system, designingparameters to be set for base stations given in plural within a servicearea, is characterized in including: an objective-function calculationstep of calculating a predetermined objective-function responding to atraffic absorption quantity and (or) a communication quality value ineach of said base stations; and a base-station parameter decision stepof deciding parameters for installing the base station responding tothis objective-function.

Another base-station cell design apparatus in accordance with thepresent invention, which is a base-station cell design apparatus for, indesigning a base-station installment in a mobile communication system,designing parameters to be set for base stations given in plural withina service area, is characterized in including: objective-functioncalculation means for calculating a predetermined objective-functionresponding to a traffic absorption quantity and (or) a communicationquality value in each of said base stations; and base-station parameterdecision means for deciding parameters for installing the base stationresponding to this objective-function.

Another program in accordance with the present invention, which is aprogram for causing a computer to execute a base-station cell designmethod of, in designing a base-station installment in a mobilecommunication system, designing parameters to be set for base stationsgiven in plural within a service area, is characterized in including: anobjective-function calculation step of calculating a predeterminedobjective-function responding to a traffic absorption quantity and (or)a communication quality value in each of said base stations; and abase-station parameter decision step of deciding parameters forinstalling the base station responding to this objective-function.

In accordance with the base-station cell design method in accordancewith the present invention, the above method is for sequentially addingthe base stations, and in this addition, a method is employed ofdefining an objective-function of which an argument is at least one ofthe traffic absorption quantity and the communication quality value toadd the base station responding to this objective-function, whereby aquantitatively correct judgment becomes possible in selecting thebase-station arrangement location.

Also, a technique of which the throughput is few is employed in theradio-wave propagation characteristic evaluation to be made in addingthe base station, and a technique of which the throughput is much, butwhich is of high-precision, more specifically, a technique such as theray tracing is applied in the radio-wave propagation characteristicevaluation to be made after addition. The result of the high-precisionradio-wave propagation characteristic evaluation, which is made afteraddition, is put to practical use for estimating the interferencequantity in selecting the arrangement location of the base station to beadded newly. This allows the quantity of a radio-wave analyticprocessing that accounts for a great majority of the base-station celldesign processing to be reduced, thus enabling a fast base-station celldesign.

Furthermore, in accordance with the base-station cell design method inaccordance with the present invention, the above method is forsequentially deleting the base stations that do not contribute to anincrease in the traffic coverage ratio from the above-mentionedadditional base-station group, and a new radio-wave analysis is notrequired for this already-installed base-station group that wasadditionally installed in sequentially deleting the base stationsbecause the high-precision radio-wave analysis has already beencompleted in the entire service area with each taken as a transmissionpoint.

The present invention having the features as mentioned above can excludethe vagueness that was at stake in the patent document 1 because amechanical processing applies without a necessity for the perception andthe experience of a person in selecting the location candidate, and canprovide the station-installment design algorithm that does not give riseto the unstable phenomenon that was at stake in the patent document 2,and yet that enables the base-station cell design with at most severaltimes of the radio-wave propagation characteristic evaluation, orsomething like it as against the base station number to be arrangedfinally.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other objects, features and advantages of the present inventionwill become more apparent upon a reading of the following detaileddescription and drawings, in which:

FIG. 1 is a view illustrating the specification of the service area, thebase-station arrangement candidate point, and the traffic distribution;

FIG. 2 is a flowchart illustrating the operation of the first embodimentin the base-station cell design algorithm of the present invention;

FIG. 3 is a view illustrating an example of the recorded contents overthe memory of the traffic absorption quantity T, the quality value Q,and the objective-function O at each base-station candidate point;

FIG. 4 is a view illustrating one example of the objective-function O;

FIG. 5 is a model-type view illustrating the embodiment of the presentinvention;

FIG. 6 is a view illustrating an additional embodiment relating to thespecification of the traffic absorption quantity T;

FIG. 7 is a view illustrating a further embodiment relating to thespecification of the traffic absorption quantity T;

FIG. 8 is a view illustrating an additional embodiment relating to thespecification of the quality value Q;

FIG. 9 is a view illustrating a further embodiment relating to thespecification of the quality value Q;

FIG. 10 is a functional block diagram illustrating the apparatusconfiguration of the first embodiment of the present invention;

FIG. 11 is a flowchart illustrating the operation of the secondembodiment in the base-station cell design algorithm of the presentinvention;

FIG. 12 is a functional block diagram illustrating the apparatusconfiguration of the second embodiment of the present invention;

FIG. 13 is a view for explaining an example of a case where awider-range cell design is made in the embodiment of the presentinvention;

FIG. 14 is a view illustrating another example of the recorded contentsover the memory of the traffic absorption quantity T, the quality valueQ, and the objective-function O at each base-station candidate point;

FIG. 15 is a view illustrating an example of a case where a plurality ofthe computers are used to perform the processing in the embodiment ofthe present invention in parallel;

FIG. 16 is a view illustrating another example of a case where aplurality of the computers are used to perform the processing in theembodiment of the present invention in parallel;

FIG. 17 is a view for explaining the prior art;

FIG. 18 is a view for explaining the additional prior art.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be explained in details belowby referring to the accompanied drawings. Firstly, the base-station celldesign algorithm of the present invention premises that the servicearea, the base-station location candidate point, and the trafficdistribution are given (for example, the traffic distribution can beestimated from the traffic quantity etc. on a road that exists within aservice area Z000-1). FIG. 1 is a view illustrating a setting example ofeach parameter thereof. Z000-1 represents the service area, and a smallblack circle Z000-2 indicates one of the base-station location candidatepoints. Also, there is also a case where the location candidate point isthree-dimensionally specified, and there is a case where a plurality ofobservation points are specified that have an identical XY coordinate,and yet have different Z-axis coordinates respectively. Furthermore,there is a case where the setting is made of the location candidatehaving even a direction of the base station considered in the event ofusing a directive antenna, and so forth. That is, for example, a casecorresponds hereto where an identical XYZ coordinate point is seasonedwith information relating to the direction of the base station, andwhere a plurality of the location candidate points are set.

In selecting the location candidate point, the location candidate pointis pre-excluded of the location where the base station is physicallyimpossible to install. Also, there is a case where the order ofinstallment priority is set for each location candidate point because alocation such that the base station should be intentionally installedmight exist. In FIG. 1, assume that geographic information such as ageographical feature, a road, building structure data, of which thedisplay was omitted in the figure, is specified in details within theservice area Z000-1 so as to estimate the high-precision radio-wavepropagation characteristic.

Domains Z000-3 and Z000-4 represent the traffic density distribution,and the traffic having a different traffic density was supposed to occuruniformly in each domain. There is a case where the traffic distributionis given non-uniformly. In the traffic distribution model shown in FIG.1, assume that no traffic occurs in the area other than the domainsZ000-3 and Z000-4. There is also a case where is excluded thebase-station location candidate point of the area in which no trafficoccurs so as to reduce the calculation amount for making the propagationcharacteristic estimation. For example, upon thinking that no trafficoccurs in the domain in which a river, a pond, etc. exist, thebase-station location candidate point can be excluded from thesedomains. However, in the event of the domain in which the stationinstallment is possible, the base-station location candidate pointthereof is not excluded (for example, Z1-6 of FIG. 5), even though notraffic occurs.

FIG. 2 is a flowchart illustrating a first embodiment of thebase-station cell design algorithm that the present invention shows. Asone example is shown in FIG. 1, assume that N (N is an integral numberequal to or more than 2) base-station location candidate points weregiven, and assume that index numbers 1 to N were allocated for thebase-station location candidate points respectively.

In a step Z0-1, an index variable A is set at 1 (one). In a step Z0-2, atraffic absorption quantity is set at T (A), and a communication qualityvalue (hereinafter, referred to simply as a quality value) at Q (A, k)in a case where it was supposed that the base-station candidate wasinstalled at the base-station location candidate point of an indexnumber A to add the cell, and respective values are computed. Here kindicates a channel number. For example, the quality value Q (A, k) iscomputed for each of four channels in the-case that four channels areavailable.

A shape of the cell to be formed by the basestation at a locationcandidate is set as a fixed shape, or is set by employing a firstradio-wave propagation characteristic estimation technique. For thisfirst radio-wave propagation characteristic estimation technique, aradio-wave propagation characteristic estimation technique, which is oflow estimation precision, but of which the calculation amount is few, isemployed. For example, a radio-wave propagation characteristicestimation model of attenuating in proportional to an exponential powerof a distance, etc. corresponds hereto. In this case, a propagationconstant of the distance attenuation is decided responding to thepropagation circumstance where the base-station cell design is made. Or,there is a case where the ray tracing technique having the precisionlowered is utilized as the first estimation technique.

The ray tracing technique is a technique to be employed in making thehigh-precision propagation estimation, and the known techniquedisclosed, for example, in Proc. of International Symposium on Antennasand Propagation Society, 1991, Vol. 3, pp. 1540-1543 (non-patentdocument 2), JP-P2002-107397A (patent document 3), etc can be used for aray-launching technique known as one packing technique thereof. In theevent of requiring this radio-wave propagation estimation technique forthe high precision, a lot of the calculation amount is needed; howeverlowering the precision allows the calculation amount to be reduced. As amethod of lowering the precision, a cutback in the reflection number ofthe radio wave, etc. is listed.

As to the traffic absorption quantity T (A), there are a case where itindicates the traffic quantity to be absorbed by the cell that thebase-station candidate forms, a case where it indicates a total quantityof the traffic quantity to be absorbed by all the cell that the abovebase-station candidate forms and the cells that the already-installedbase stations form respectively, a case where the traffic quantity isemployed that occurs within the area to be covered by the additionalbase-station candidate to be computed by the traffic densitydistribution, a case where the traffic quantity is employed that occursin the area other than the area covered by the already-installed basestations, out of the areas to be covered by the additional base-stationcandidate to be calculated by the traffic density distribution, and soforth. Also, there is also a case where each said quantity is given witha rate as against a total traffic quantity that occurs within theservice area.

As to the quality value Q (A, k), there are a case where it indicates anaverage of the quality values to be observed in the cell that thebase-station candidate forms, a case where it indicates a rate at whichthe quality to be observed in the cell that the above base-stationcandidate forms, and the cells that the already-installed base stationsform, respectively, satisfies a desired value, and a case where itindicates an average value of the above quality. Herein, as to theso-called quality value, there are a case where it is given as a desiredreceived signal power/(an undesired received signal power + a noisesignal power) at the observation point, a case where it is given as thedesired received signal power/the undesired received signal power at theobservation point, and a case where it is given as various error ratessuch as a bit error rate and a frame error rate at the observationpoint. Furthermore, as to the quality value Q (A, k), there are a casewhere it is specified by the traffic quantity that occurs in the area inwhich the quality, which is observed in the cell that the abovebase-station candidate forms and in the cells that the already-installedbase stations form, respectively, satisfies a desired value, and a casewhere it is specified by a rate of said quantity to the traffic quantitythat occurs in the entire service area. The quality value Q is checkedfor all channels that the system can allocate.

Next, in a step Z0-3, an objective-function O (T (A), Q (A, k)) of whichan argument is the traffic absorption quantity T (A), and the qualityvalue Q (A, k) is computed to store it in a memory. Contents recorded inthe memory in this case are ones as shown in FIG. 3. That is, T (A), Q(A, k), and O ((A), Q (A, k)) are to be recorded respectively,responding to four channels k=1 to 4 respectively at each base-stationcandidate point to be shown with an index number A (shown as A1, A2, . .. ).

Herein, as to the value of the objective-function O to be recorded,there are a case where it is specified only by the traffic absorptionquantity T, and a case where it is specified only by the quality valueQ. An example of the objective-function O will be described later byreferring to FIG. 4.

In a step Z0-4, it is determined whether the index variable A is lessthan a base-station location candidate point number N, and if A<N, in astep Z0-5, then the steps subsequent to the step Z0-2 are repeated after1 (one) is added to A. If A≧N in a step Z0-4, then the process proceedsto a step Z0-6. In the step Z0-6, the objective-function of which thevalue becomes maximum is to be selected from among all recorded ones todecide to locate the base station at the base-station arrangementlocation candidate point having the index number of the aboveobjective-function, and the channel number of the aboveobjective-function is allocated for the above base station.

In a step Z0-7, with the base station for which installment was newlydecided in the step Z0-6 taken as a transmission point, the radio-wavepropagation characteristic is estimated in the entire service area torecord it. Herein, the second radio-wave propagation characteristicestimation technique is employed for estimating the radio-wavepropagation characteristic. A technique, of which the estimationcalculation amount is much, but which is of high estimation precision ascompared with the first radio-wave propagation characteristic estimationtechnique, is employed for the second radio-wave propagationcharacteristic estimation technique. For example, the high-precisionradio-wave propagation characteristic analytic technique such as the raytracing corresponds hereto. An estimation result is recorded in amemory, a disk, etc. As one example of the estimation result are listeda received electric power (or propagation loss), or the receivedelectric power (or propagation loss) and a delay spread, or a pathprofile that is composed of a delay time and the received electric power(or propagation loss) for each arrived pass at each observation point,and so forth.

In a step Z0-8, by making a reference to the estimation result of theradio-wave propagation characteristic computed and stored by the secondradio-wave propagation characteristic estimation technique, which isrelated to all base stations for which installment was decided thus far,the transmitted power of each base station, and the area (cell) thateach base station covers are found to compute the traffic coverage ratioRc. A cell is defined as a group of minute areas into which the servicearea is divided. Those minute areas belong to the cell covered by a basestation when the minute areas have the minimum propagation loss anddesired received quality for the base station.

Herein, the size/shape of each cell varies with not only the radio-wavepropagation characteristic, but also the setting of the transmittedpower and a received threshold of each station. The so-called receivedthreshold herein is a threshold in performing a demodulation processingin a receiver, and the demodulation is performed only when the receivedsignal satisfies the above threshold. The received threshold is known asa CSMA threshold, a receiver threshold, etc. in a carrier sense multipleaccess (CSMA) technique that has been put to practical use in thewireless LAN, etc. It is necessary to set the transmitted power of thebase station, and (or) the received threshold as well simultaneously infinding the covered area of each base station. The larger thetransmitted power is, and the lower the received threshold is, thelarger cell spreads, which leads to an increase in the traffic thatoccurs within the cell.

However, there is the upper limit to the traffic quantity that can beprocessed in one base station. Therefore by operating the transmittedpower and (or) the received threshold, the traffic quantity inside thecell is set to be less than the maximum traffic quantity that can beprocessed in one base station. In addition, as to the transmission powerand the received threshold, there is the range thereof in whichrespective values can be set, whereby regulation is made within therespective setting ranges in operating both parameters.

In computing this traffic coverage ratio Rc, the channel allocation forthe base station of which installment was newly decided also can berechecked. The reason is that the channel reallocation by employing themore precise propagation characteristic by the second propagationcharacteristic estimation technique can provide more interferencetolerance. Because the channel allocation for which installment wasnewly decided was employed by the first propagation estimationtechnique. The re-checking processing of the channel allocation isperformed as follow. At first, the objective-function is re-computed onthe supposition that the newly installed base station used each channelaccording to the propagation characteristic estimated by the secondpropagation characteristic estimation technique. The channel of whichthe objective-function becomes maximum is used among respectivechannels.

After the transmission power of each base station installed as mentionedabove, and the size/shape of the area that the above base stationdefended were decided, a rate of a total traffic to be absorbed by thebase station group for which installment was decided to a total trafficquantity that occurs within the entire service area is found to specifythis as a traffic coverage ratio Rc.

In a step Z0-9, the traffic coverage ratio Rc is compared with arequired traffic coverage ratio Rth, if Rc≦Rth, then the processingreturns to the step Z0-1, and if Rc>Rth is satisfied, then thebase-station installment processing is completed (a step Z0-10).

The first embodiment of the present invention explained by use of FIG. 2is characterized in sequentially adding the base stations one by one.Taking the traffic quantity into consideration in the stage of addingthe base station enables the appropriate base-station cell design thatresponded to roughness/fineness of the traffic quantity, thus allowingthe propagation quality to be prevented from deteriorating due tocongestion. Also, the cell design having high tolerance against theinterference is achieved possible because the cell design, which tookthe interference quantity into consideration, is made with the secondradio-wave propagation characteristic estimation such as the ray tracingforecasted in high precision. The second radio-wave propagationcharacteristic estimation evaluation, which is of high precision butrequires a lot of the calculation amount, is made after the base-stationarrangement location was decided, and the first radio-wave propagationcharacteristic estimation technique of which the calculation amount isfew is employed at the time of the additional base-station searchprocessing.

That is, in accordance with the present invention, the high-precisionradio-wave propagation characteristic evaluation extending over theentire service area should be executed only for the base station to beinstalled finally, which enables a reduction in the time required forthe base-station arrangement design, as compared with the technique ofthe non-patent document 1 that requires the high-precision radio-wavepropagation characteristic evaluation extending over the entire servicearea for all base-station candidate points. Furthermore, as comparedwith the prior art disclosed in the patent document 1, the presentinvention enables the cell design having always a constant effectwithout a help of the experience/perception of design experts. Also, ascompared with the prior art disclosed in the patent document 2,similarly to the comparison with the non-patent document 1, the effectsuch that a drastic reduction in the design processing time is achieved.

FIG. 4 is a view illustrating one example of the objective-function Owith the traffic absorption quantity T and the quality value Q taken asan argument. The setting is made so that the higher the trafficabsorption quantity T is, and the higher the quality value Q is, thelarger the objective-function becomes. Introduction of theobjective-function shown in FIG. 4 allows two evaluation indexes of thetraffic absorption quantity and the quality value to be integrated forhandling at the time of the base-station cell design.

In addition, as an example of the objective-function O,

O=Q*T, or

O=a*Q+b*T(a and b are a constant), or

O=α*Q+(1−α)*T (α is a weighted coefficient, and 0<α<1), and so forth,can be assumed; however it is not limited hereto. In addition, *represents multiplication in each above-mentioned equation.

Furthermore, in the event that an installment priority P was set foreach of the location candidate points, there is a case where theabove-mentioned objective-function O is further multiplied by theinstallment priority P (or the installment priority P is added afterweighting) to employ this as an objective-function. As the case may be,the objective-function O has an identical value, even though A (locationcandidate point), and k (channel) thereof are different respectively.This could happen because the traffic absorption quantity of each basestation is limited to the maximum traffic that the base station canaccommodate. For this, as a secondary judgment stuff, a differentobjective-function O′ (T′, Q′) is sometimes employed. For example, notby taking the maximum traffic that AP can accommodate into considerationin T′ in the objective-function O′, O′ different from theobjective-function O can be employed as a secondary judgment stuff.

Next, how the objective-function O is found for a certain base-stationcandidate will be explained specifically. FIG. 5 is a view explainingthe situation where the objective-function O is decided in the presentinvention in a model-type manner. In FIG. 5, a service area Z1-1 isgiven, and the traffic distribution is given like domains Z1-7 and Z1-8shown with oblique lines within the service area Z1-1. The domains Z1-7and Z1-8 differ in a traffic occurrence density. A black small circleZ1-9 indicates the base-station location candidate point, black squaresZ1-4 to Z1-6 indicate the already-installed base stations, or the basestation for which installment was decided in the step Z0-6 of FIG. 2 byemploying a method relating to the present invention. A white squareZ1-2 indicates the base-station candidate installed at a certainlocation candidate point, and how the objective-function O can be foundfor the base-station candidate will be explained below.

At first, a cell Z1-3 that the above base-station candidate Z1-2 formsis specified. At this time, the shape of the cell Z1-3 can be found inthe step Z0-2 of FIG. 2. As to the cell Z1-3, there is a case where afixed shape is pre-allocated for it, and a case where it is decided bythe transmitted power that the above base-station candidate Z1-2 emits,and the propagation loss to be obtained by said first radio-wavepropagation characteristic estimation technique. In the latter case, thetransmitted power is decided as follows. That is, the transmitted poweris the transmitted power regulated so that the traffic quantity thatoccurs within the cell becomes the maximum traffic quantity that onebase station can process, or the maximum transmitted power, whichever islower.

As one example of how to find the transmission power, the following canbe considered. At first, suppose the cell at the time that thetransmission power was maximized to calculate the traffic quantity to beabsorbed within the above cell, if this calculated traffic quantity isfewer than the maximum traffic quantity that one base station canprocess, to assume that the transmitted power is the maximum power ofthis base station, and to assume that the cell is the above-mentionedcalculated cell. Also, when the above calculated traffic quantity islarger than the maximum traffic quantity that one base station canprocess, assume the transmission power, which is enough to cover thecell that absorbs the traffic that corresponds to this maximum trafficquantity, to be a transmitted power of this base station.

The traffic absorption quantity T is equivalent to a total quantity ofthe traffic that occurs inside the cell Z1-3. That is, it is the trafficquantity that occurs in respective portions of the domains Z1-7 and Z1-8to be included inside the cell Z1-3.

The quality value Q, which is given as a function of the total sum ofthe interference quantities from the already-installed base stationsZ1-4 to Z1-6 that are received in the location candidate Z1-2, isdefined so that the lower the total sum of the interference quantitiesis, the higher it becomes. For example, the quality value Q is definedso as to be inversely proportional to the total sum of the interferencequantity. The interference quantity from each of the already-installedbase stations Z1-4 to Z1-6 is decided by those interference transmissionpower and the propagation loss up to the location candidate. As to theinterference-wave transmitted power, there are a case where the fixedvalue is employed for it, and a case where it is set in proportional tothe size of the traffic to be loaded on the above already-installed basestation. The result of the high-precision propagation-loss estimationcomputed and stored by said second radio-wave propagation characteristicestimation technique is applied for the propagation loss from each abovealready-installed base station up to the location candidate point.

After the traffic absorption quantity T and the quality value Q werefound as mentioned above, the calculation is performed with theobjective-function O exemplified in FIG. 4.

In accordance with the embodiment relating to the objective-function Odecision explained in FIG. 5, the base-station cell design becomespossible that took into consideration the traffic quantity that occurswithin the cell to be formed by the base-station candidate, and theinterference quantity that is received in the above base station. Thisembodiment is characterized in that, in the event that the base stationis installed at the base-station location candidate point, thebase-station installment is made more preferentially for the installmentlocation in which the traffic quantity is processed the more by theabove base station, or the less the interference quantity is.

FIG. 6 is a view illustrating an additional embodiment relating to thespecification of the traffic absorption quantity T in FIG. 5. In FIG. 6,Z2-1, Z2-4, and Z2-5 indicate the already-installed base stations, orthe base station for which installment was decided in the step Z0-6 ofFIG. 2 employing a method relating to the method of the presentinvention, respectively, and Z2-9 indicates the base-station candidate.The cells to be formed by the already-installed base stations of Z2-1,Z2-4, and Z2-5 are Z2-2, Z2-3, and Z2-6 respectively, and the cell to beformed by the base-station candidate Z2-9 is Z2-10.

It is supposed that, in deciding the cells to be formed by thealready-installed base stations (Z2-1, Z2-4, and Z2-5), the result ofthe high-precision propagation-loss estimation computed and stored bysaid second radio-wave propagation characteristic estimation technique(Z0-7 of FIG. 2) is applied, and also, that the appropriate base-stationselection is employed in each minute area within the service area.Herein, the so-called base-station selection for each minute areaindicates an action of, in the event that a terminal was assumed toexist in a certain minute area, connecting to the base stationsatisfying a desired received quality, and having the minimumpropagation loss, or an action of connecting to the base stationsatisfying a desired received quality that can realize communication ofwhich the received quality or the received signal power is high. Thatis, the above base-station selection is made, thereby allowing formationof a cell boundary such that the best communication quality can beassured in each location within the service area.

However, each minute area does not select the base-station candidateZ2-9 at the time of selecting the base station, and the cell boundary ofthe base-station candidate Z2-9 assumes a fixed shape, or a shape likeZ2-10 to be found by said first radio-wave propagation characteristicestimation technique. The traffic that occurs within the cell formed insuch a manner is to be absorbed by the base station that takes charge ofthe above cell.

In addition, the limit value is set at the traffic quantity that onebase station can accommodate, and the traffic quantity that occurswithin the cell found above, or the allowable traffic quantity of thebase station, whichever is lower, can be assumed to be the trafficquantity to be accommodated in the above cell.

An additional embodiment relating to the specification of the trafficabsorption quantity T shown in FIG. 6 is characterized in, at the timeof calculating the traffic absorption quantity T for a cell Z2-10,excluding the traffic that occurs in the domains Z2-7, and Z2-8 that thealready-installed base stations Z2-4 and Z2-5 have already covered.Excluding the traffic already absorbed by the already-installed basestations from the traffic quantity T to be loaded on the base stationthat is newly added allows more correct traffic quantity T to beestimated.

FIG. 7 indicates a further embodiment relating to the specification ofthe traffic absorption quantity T. In FIG. 7, Z6-1, Z6-4, and Z6-5indicate the already-installed base stations, or the base station forwhich installment was decided in the step Z0-6 of FIG. 2 by employing amethod relating to the method of the present invention, respectively,and Z6-9 indicates the base-station candidate. The cells to be formed bythe already-installed base stations Z6-1, Z6-4, and Z6-5 are Z6-2, Z6-3,and Z6-6 respectively, and the cell to be formed by the base-stationcandidate Z6-9 is Z6-10. In deciding the cells to be formed by thealready-installed base stations, the result of the high-precisionpropagation-loss estimation computed and stored by said secondradio-wave propagation characteristic estimation technique (Z0-7 of FIG.2) is applied. Also, the cell to be formed by the base-station candidateZ6-9 is found by employing the result of the propagation characteristicestimation to be computed by said first radio-wave propagationcharacteristic estimation technique. It is supposed that the appropriatebase-station selection is employed in each of minute area within theservice area.

Herein, the so-called base-station selection for each minute areaindicates an action of, in the event that a terminal was assumed toexist in a certain minute area, connecting to the base stationsatisfying a desired received quality and having the minimum propagationloss, or an action of connecting to the base station satisfying adesired received quality that can realize communication of which thereceived quality or the received signal power is high. That is, theabove base-station selection is employed, thereby allowing formation ofa cell boundary such that the best communication quality can be assuredin each location within the service area. The traffic that occurs withinthe cell formed in such a manner is to be absorbed by the base stationthat takes charge of the above cell.

In addition, the limit value is set at the traffic quantity that onebase station can accommodate, and the traffic quantity that occurswithin the cell found above, or the allowable traffic quantity of thebase station, whichever is lower, can be assumed to be the trafficquantity to be accommodated in the above cell.

A further embodiment relating to the specification of the trafficabsorption quantity T shown in FIG. 7 is characterized in assuming atotal quantity of the traffic to be absorbed by the already-installedbase stations Z6-1, Z6-4, and Z6-5, and the base-station candidate Z6-9to be the traffic absorption quantity T.

The traffic absorption quantity T is defined as a total quantity of thetraffic to be absorbed by the already-installed base stations and thebase-station candidate within the service area. Hence, a base stationcandidate that can absorb maximum traffic quantity accompanied withalready installed base stations is selected to be newly added.

FIG. 8 is a view illustrating an additional embodiment relating to thespecification of the quality value Q in FIG. 5 in a model-type manner.Suppose an evaluation terminal Z3-6 indicated with a white triangle,which connects to a base-station candidate Z3-5 indicated with a whitesquare, to specify the quality value Q with a ratio of the desiredreceived signal power and the undesired received signal power (DU ratio)to be observed in the above evaluation terminal Z3-6. The propagationloss to be computed by said first radio-wave propagation characteristicestimation technique is employed in computing the desired signal power.In the event of, as the first radio-wave propagation characteristicestimation technique, employing a distance attenuation value thatattenuates in proportional to an exponential power of a distance, alinear distance Z3-10 from the base-station candidate Z3-5 up to theevaluation terminal Z3-6 is employed as a distance.

Z3-1 to Z3-3 indicate the already-installed base stations, or the basestation for which installment was decided in the step Z0-6 of FIG. 2 byemploying a method relating to the method of the present invention,respectively. The undesired signal power is decided by the propagationloss from each of the base stations Z3-1 to Z3-3 up to the evaluationterminal Z3-6, and the undesired signal transmission power that eachalready-installed base station emits. As to the undesired signaltransmission power to be emitted from each of the already-installed basestations Z3-1 to Z3-3, there are a case where it is assumed to be fixed,and a case where it is decided responding to the traffic quantity to beloaded on each already-installed base station. The high-precisionpropagation-loss value estimated and stored by said second radio-wavepropagation characteristic estimation technique is employed for thepropagation loss from each already-installed base station up to theevaluation terminal.

Said evaluation terminal Z3-6 is assumed to be in each location withinthe cell Z3-4 that said base-station candidate Z3-5 forms to find saidDU ratio, and the quality value Q is specified by averaging it. At thismoment, there is a case where the location within the above cell Z3-4 inwhich no traffic occurs is not assumed to be an object of the averagingprocessing. Or, there is a case where a weighting is made responding tothe size of the traffic density within the above cell Z3-4 for averagingit.

In accordance with an additional embodiment relating to thespecification of the quality value Q shown in FIG. 8, employing the DUratio to be observed in a virtual evaluation terminal for the qualityvalue to average it within the cell that the base-station candidateforms enables the more strict quality evaluation that took an extensiveview within the cell in terms of the plane.

FIG. 9 is a view illustrating a further embodiment relating to thespecification of the quality value Q in FIG. 5 in a model-type manner.The entire region within the service area is scanned with an evaluationterminal Z4-4 to find the DU ratio in each evaluation-terminalarrangement location, and to specify a ratio satisfying a desired DUratio as the quality value Q. Assume that the evaluation terminal isconnected to the already-installed base station, or the base-stationcandidate that can make communicate with the highest receiving signalpower from the location in which the above terminal was installed, andthat the interference signal power is the total sum of the undesiredsignal powers from the already-installed base stations and the basestation candidate other than the base station assumed to connect to theabove terminal. The above quality value is defined so that the smallerthis total sum is, the higher the quality value becomes.

In an example of FIG. 9, an evaluation terminal Z4-4 connects to analready-installed base station Z4-2, thus the interference signalsarrive at the evaluation terminal Z4-4 from already-installed basestations Z4-1 and Z4-3, and a base-station candidate Z4-5. There is acase where a location within the service area in which no traffic occursis not assumed to be an object of evaluation for measuring the qualityvalue Q. Or, there is a case where the quality value Q is specified byperforming weighted addition of the DU ratio responding to the size ofthe traffic density within the service area.

The propagation loss from the base-station candidate to the evaluationterminal is given with the propagation loss to be computed by said firstradio-wave propagation characteristic estimation technique. Thepropagation loss value between the already-installed base station andthe evaluation terminal is estimated and stored by said secondradio-wave propagation characteristic estimation technique. As to theundesired signal transmission of each already-installed base station andthe base-station candidate, there are a case where it is assumed to befixed, or a case where it is decided responding to the traffic quantityto be loaded on each base station.

In accordance with a further embodiment relating to the specification ofthe quality value Q shown in FIG. 9, the base-station cell designachieves that, in adding the base station candidate, took intoconsideration not only the quality value to be observed within thebase-station candidate, but also an influence of the qualitydeterioration to be observed in the other cells due to addition of theabove base-station candidate.

FIG. 10 is a view illustrating a cell design apparatus D001 forrealizing an operational flow shown in FIG. 2 as a schematic functionalblock. As input information 1 are listed map information, trafficdistribution information, base-station installment candidate pointinformation, and the required traffic coverage ratio Rth (see the stepZ0-9 of FIG. 2) of the service area. An objective-function O measurementrecord section 2 calculates the traffic absorption quantity T and thequality value Q, employing a first radio-wave propagation estimationengine 3 for executing the foregoing first radio-wave propagationestimation technique, calculates the objective-function O responding tothese T and Q, and records it in a memory section (particularly, notshown in the figure) in such a manner as shown in FIG. 3.

A base-station installment/radio-wave propagation characteristicevaluation section 4 decides to install the base station at thebase-station location candidate point having the maximumobjective-function O obtained, employs a second radio-wave propagationestimation engine 5 for executing the foregoing second radio-wavepropagation estimation technique, estimates the radio-wave propagationcharacteristic within the service area with the base station, for whichinstallment was newly decided taken as a transmission point, and recordsit in the memory section.

A traffic coverage ratio evaluation section 6 finds the transmissionpower of each base station and the area that each base station covers,and calculates the traffic coverage ratio Rc. A cell design finishdetermination section 7 determines whether the traffic coverage ratio Rcexceeds a required traffic coverage ratio Rth, and when it exceeded,makes determination-as to the cell design finish. And, the parametersetting result such as the base-station arrangement result, the channel,and the transmission power is output as output information 8.

FIG. 11 is a flowchart illustrating a second embodiment in thebase-station cell design algorithm of the present invention. This secondembodiment is characterized in being performed continuously after theprocessing described in the first embodiment of FIG. 2. A step Z5-1indicates the entire processing of the first embodiment described inFIG. 2. After the processing described in the first embodiment wascompleted, in a step Z5-2, a modified traffic coverage ratio Rm that isa traffic coverage ratio in a case where each of the already-installedbase station was deleted is calculated to find a difference between thetraffic coverage ratio Rc of final result from the first embodiment ofFIG. 2 and Rm, and to find a base station D of which Rc−Rm is minimum.

At this time, Rm is found by employing the estimation result found inZ0-7 of FIG. 2 by employing the second radio-wave propagation estimationtechnique. As one example, Rm can be calculated as follows. First, analready-installed base station is assumed to be deleted. And a rate of atotal quantity of the traffic that covered by the rest of all thealready-installed base station to a total traffic quantity in the entireservice area.

As a substitute for this step Z5-2, that is, instead of selection of thebase station of which Rc−Rm is minimun, the objective-function O (T, Q)in a case where each base station was deleted may be computed to selectthe base station of which the objective-function O is maximum at thetime that it was deleted as a deletion candidate base station. In thiscase, the traffic coverage ratio Rm in a case where the base stationselected based on the objective-function was deleted is computed, andthe processing proceeds to the next step.

In a step Z5-3, it is determined whether or not the modified trafficcoverage ratio Rm in a case where it was assumed that the base station Dwas deleted is still more than the threshold Rth of the traffic coverageratio. If Rm>Rth is satisfied, then the base station D is deleted fromthe already-installed base station group in a step Z5-4, and if it isnot satisfied, then the processing proceeds to a step Z5-6, and thebase-station cell design is finished.

After the base station D was deleted in the step Z5-4, the transmissionpower of each base station and the area covered by each base station arefound once again in a step Z5-5 to re-compute the traffic coverage Rc.The detailed processing in the step Z5-5 is identical to the processingof the step Z0-8 in the first embodiment described in FIG. 2. After thestep Z5-4 was finished, the steps subsequent to Z5-2 are repeated onceagain.

The second embodiment of the present invention explained in FIG. 11allows the useless base station to be deleted out of the base stationsinstalled in the first embodiment. In the first embodiment described inFIG. 2, there is the possibility of the occurrence of the base stationthat results in being uselessly installed due to employing the firstradio-wave propagation characteristic estimation technique, which needsa small amount of calculations while having low estimation precision,that is, the base station that does not contribute to an improvement inthe traffic coverage ratio so much. The second embodiment allows thebase station arrangement having a least sufficient number to berealized, by deleting such a useless base station.

FIG. 12 is a view illustrating a cell design apparatus D002 forrealizing an operational flow shown in FIG. 11 as a schematic functionalblock, and the identical portions to FIG. 10 are indicated withidentical numerals. The cell design apparatus D002 is connected to therear stage of the cell design apparatus D001 shown in FIG. 10 foroperation, and deletion base-station decision section 9 receives theoutput of the cell design apparatus D001 of FIG. 10, and decides whichbase station should be deleted. This technique of the deletionbase-station decision is the processing of the step Z5-2 to Z5-5 in aflow of FIG. 11.

A cell design finish determination section 10 determines the finish ofdeletion base-station decision, and also, a base-station deletionsection 11 deletes the base station decided in the deletion base-stationdecision section 9. Final output information 8′ is obtained in such amanner, and the parameter setting result such as the base-stationarrangement result, the channel, and the transmission power is obtained.The parameter setting result is made from the output information 8 shownin FIG. 10 by deleting some base stations in the base-station deletionsection 11.

There is a case where the cell design should be made for the area widerthan the area explained by employing FIG. 5 to FIG. 9. As to the celldesign technique of the present invention in such a case, one examplethereof will be explained by employing FIG. 13. FIG. 13 is a viewillustrating a case where the cell design is made for the area widerthan that of FIG. 5 etc. The design area shown in FIG. 13 is dividedinto two areas X01 and X02 that are overlapped with each other. Atfirst, the cell design is executed for the area X01 by the cell designtechnique of the present invention mentioned above. The-base-stationgroup designed in such a manner is shown as X03-i (i=1 to 4) in FIG. 13.

After designing the area X01, next, the area X02 is designed. The areaX02 shown with a bold frame is overlapped with the area X01 shown with afine frame, and base stations X03-4, and X03-3 designed already in theX01 are included in the area X02. In designing the area X02, the basestations X03-3 and X03-4 are considered as the already-installed basestation to make the cell design for the location candidate point otherthan the above base-station installment location according to theforegoing cell design procedure.

For example, in the event of make the cell design for the entire region,and so forth, the cell design has to be made for an enormous number ofthe base-station location candidates, whereby it is anticipated that thememory and the necessary computation quantity becomes enormous. Also inthe event of making such a wide-range cell design, in accordance withthe present invention, extracting a plurality of the areas divided intosmall pieces allows the reduction of the quantity of the memory and thecomputation to be achieved. At this moment, by causing themutually-neighboring area companions to overlap intentionally in makingthe cell design for a certain cell A, the cell design, which took theinterference from the already-installed base station into consideration,becomes possible in a area B neighboring A.

Also, in the event that the base station was already installed as amatter of fact in the service area taken as an object, if the foregoingcell design in accordance with the present invention is made uponpresetting the location information, setting channel information,transmission power information, etc. of the above base station, thedesign of the new-addition base station after due consideration of theseinterferences becomes possible.

Also, as described in the above, there is a case where informationincluding the XYZ coordinates and the installation direction is given asthat of a base-station location candidate point; however in the eventthat the type of the usable antenna is plural, the receivedcharacteristic differs depending upon the type and the installationdirection of the antenna. For this, in the event that the type of theusable antenna is plural, computing the objective-function with the typeand the installation direction of the antenna taken as a parameterenables a more detailed design. In this case, in the mentioned above,the communication quality value Q (A, k) was defined as a function of alocation A in which the base station was installed, and a channel k tobe used; however, as Q (A, k, t, d), a type of an antenna t and aninstallation direction d of the base station have to be added as anelement.

The processing flow will be explained in a case where the communicationquality value is assumed to be Q (A, k, t, d), based on FIG. 2. In thestep Z0-2 of FIG. 2, the quality value Q is computed for allcombinations of the base-station location candidate point A, the channelk, the type of the antenna t, and the installment direction d. Also, theobjective-function to be computed in the step Z0-3 amounts to O (t (A),Q (A, k, t, d)), and the contents recorded in the memory are ones shownin FIG. 14. That is, T (A), Q (A, k, t, d), and O (T (A), Q (A, k, t,d)) are to be recorded respectively responding to the channel k, thetype of the antenna t, and the installation direction d at eachbase-station candidate point indicated with the index number A (shown asA1, A2, . . . ) respectively.

This example illustrates a case where the number of channel is three,the number of the antenna type is two, the number of installmentdirection is two patterns for the antenna t=1, and the number ofinstallation direction is four patterns for the antenna t=2. The numberof installation direction depends on the sharpness of antennadirectivity. For example, in the event of the non-directional antenna,the pattern thereof is only one (1) because it does not make sense tocause the installation direction to vary. In the step Z0-6, theinstallment-location candidate point at which the maximumobjective-function is obtained, the channel, the type of the antenna,and the installation direction are set for the above base station.

Also, in the cell design apparatuses D001 and D002 shown in FIG. 10 andFIG. 12 respectively, in the event that the type of the antenna and theinstallation direction were added as an element of the quality value Q,the type of the antenna and the installation direction also aresimultaneously output as the output information 8 and 8′ in addition tothe base-station arrangement result, the channel, the transmissionpower, etc.

Computation of the objective-function in a manner mentioned above allowsthe appropriate antenna to be select from the type of the antenna thatis selectable in plural and the appropriate installation direction ofthe antenna to be decided.

Also, as the case may be, in the present invention, there rises anecessity for still performing a lot of the computation processing,depending upon the number of the base-station location candidate pointand the received-quality observation point, although the reduction ofthe computation processing time is realized, as compared with the priorart. So as to further reduce the time required for this processing, theprocessing program for executing the present invention can be modifiedto a parallel-computable form. Upon performing the parallel computation,the computation time can be reduced because the computation can beperformed simultaneously by employing plural computers. After theparallel computation was performed, the result obtained by each computeris collected to continue the processing. The processing item in thesteps Z0-1 to Z0-5 in FIG. 2 where the first radio-wave propagationcharacteristic estimation technique is employed to search for theparameters for obtaining the maximum objective-function can be executedeffective by parallel computing.

There is a necessity for calculating the propagation analysis by thefirst propagation estimation technique between all points at which thetraffic exists (assumed to be a T point) and the base-station locationcandidate point. The flow shown in FIG. 2 was described that thepropagation characteristic was calculated by the first radio-wavepropagation characteristic estimation technique whenever each of thequality value Q and the traffic absorption quantity T were calculated;however a packing thereof takes a form of pre-calculating thepropagation characteristic, to record it, and at the time of calculatingthe quality value Q and the traffic absorption quantity T to draw outthe recorded value for employing it. This propagation characteristiccomputation employing the first radio-wave propagation estimationtechnique with all base-station location candidate points taken as atransmission point can be performed in the parallel processing becausethe propagation characteristic can be computed independently at eachbase-station location candidate point. Also, as to the computation ofthe objective-function, it can be performed in a parallel processingbecause the objective-function can be computed independently for eachinstallment condition. Hereinafter, the technique of the parallelprocessing will be described in details.

The subject number for finding the propagation characteristic numbers anoccurrence point number N of the traffic and a base-stationinstallment-location candidate point number M. Like FIG. 15, there existN*M kinds of the propagation characteristics that should be found,ranging from a propagation characteristic 11 to a propagationcharacteristic NM (*signifies multiplication). This is divided by aparallel-processable computer number P to compute an N*M/P portion ofthe propagation characteristic respectively. By connecting the resultsobtained by respective computers, all the result of propagationcharacteristics 11 to NM can be obtained. So as to connect the result ofthe parallel processing, an overhead for communication is required,whereby a is added to the computation time in the figure.

Also, in the event that the computing capability of the computer forperforming the parallel processing differs, when the processing amountis divided identically for allocation, the time that the result isobtained differs greatly, and until a computer of which the computingspeed is slow gains the result, the other computer resource becomesuseless sometimes. For this, a method can be employed of dividing theobject that requires the computation into smaller units (at least everyone propagation characteristic) for each computer, at the stage that theresult for small unit was obtained, to sequentially process the otherunit that has not been computed yet (see FIG. 16).

The objective-function calculation for each installment parameter has tobe performed by the pattern number of the installment-location candidatepoint number (M)×the channel number (C)×the kind number of the antenna(T)×the installment direction number (D). So as to perform thiscalculation at a high speed, similarly to the foregoing, the parallelprocessing by the computer is performed. All pattern numbers amount toM*C*A*D, whereby in the event of employing the computer group having anidentical processing capability (computer number P), M*C*A*D/P of theprocessing is allocated for each computer for computation. In the eventof using the computers having different processing capabilities, theprocessing is performed similarly to FIG. 16.

As mentioned above, by the estimation employing the first propagationcharacteristic estimation technique, and by performing the calculationof the objective-function in the parallel processing, the reduction ofthe computation time can be realized.

Also, the present invention also can be used for deciding the channel,the transmission electric power, the type of the antenna, theinstallation direction etc. for the base station preinstalled actually.This can be realized by designating the layout of the already-installedbase station as a base-station location candidate point to assume thatthe determination criteria of the step Z0-9 in FIG. 2 is not the trafficcoverage ratio, but the completion of the installation for allbase-station location candidate points. As a result, it is possible todesign the channel, the transmission power, the type of the antenna, andthe installation direction at each base station so that they have theappropriate values respectively.

In this method, there is no necessity for making the propagationestimation with a large number of the base-station location candidatepoints taken as a transmission point because the installment location ofthe base station has been pre-decided. Thus, by making the propagationestimation not by employing the first propagation estimation technique,but by employing only the second propagation estimation technique in thestep Z0-2, the more correct propagation estimation result can bereflected.

In addition, in the above-mentioned embodiment, the service area wasexplained as a two-dimensional one; however this is an example forfacilitating the grasp of the contents, and the three-dimensional spaceis similarly applicable for it. Also, needless to say, the configurationcan be made so that a flow of each operational processing mentionedabove is pre-filed in the record medium as a program to cause thecomputer to read this for execution.

The design method of the present invention does not need the perceptionand the experience of a human being because the method can makequantitative judgment by defining and using the objective-function ofwhich the argument is at least one of the traffic absorption quantityand the communication quality value to add the base station.

Also, in accordance with the present invention, the effect exists ofreducing the quantity of the radio-wave analysis processing thataccounts for a majority of the cell design processing, and of enablingthe fast base-station cell design. Because, the invention employs atechnique of which the calculation amount is few for the radio-wavepropagation characteristic evaluation to be used in selecting the basestation that should be added from all of the base-station candidates andemploys a technique of which the calculation amount is much, butprovides high precision for the radio-wave propagation characteristicevaluation to be made after the selection and put the result of thehigh-precision radio-wave propagation characteristic evaluation to bemade for estimating the interference quantity in selecting thearrangement location of the base station to be added subsequently.

Furthermore, in accordance with the present invention, deleting the basestations sequentially that do not contribute to an increase in thetraffic coverage ratio from the above-mentioned additional base-stationgroup allows the base-station arrangement having a least sufficientnumber to be realized. And as it is not necessary to make a newradio-wave analysis for this already-installed base-station group, insequentially deleting the base stations because the high-precisionradio-wave analysis has been completed in the entire service area witheach already-installed base station taken as a transmission point, thedesign by the present invention can be performed at a high speed.

1. A base-station cell design method adapted so that, in cell designingbase-station installment in a mobile communication system, a pluralityof base-station candidate locations are given within a service area tolocate base station in anyone of these base-station candidate locations,said base-station cell design method comprising the steps of: anobjective-function calculation step of calculating a predeterminedobjective-function responding to a traffic absorption quantity and (or)a communication quality value of said base-station candidate locations;and a base-station layout decision step of deciding a layout at whichthe base station is installed responding to this objective-function. 2.The base-station cell design method according to claim 1, saidbase-station cell design method characterized in being adapted so that:in said objective-function calculation step, the higher said quantityand (or) quality are, the higher objective-function is given; and insaid base-station layout decision step, a location of which saidobjective-function is highest is decided. 3-4. (canceled)
 5. Abase-station cell design method adapted so that, in cell designing in amobile communication system, a plurality of base-station candidatelocations are given within a service area to decide anyone of thesebase-station candidate locations as a base-station layout while aradio-wave propagation characteristic estimation technique is used, saidbase-station cell design method comprising the steps of: as a radio-wavepropagation characteristic estimation technique within said service areawith each of said base-station candidate locations taken as atransmission point, using a first radio-wave propagation characteristicestimation technique having a first precision; and as a radio-wavepropagation characteristic estimation technique within said service areawith a base-station location after a case where said base station wasdecided taken as a transmission point, using a second radio-wavepropagation characteristic estimation technique having a precisionhigher than said first precision.
 6. The base-station cell design methodaccording to claim 5, said base-station cell design method characterizedin: as said first radio-wave propagation characteristic estimationtechnique, employing a technique that an electric power attenuates inproportional to an exponential power of a distance; and as said secondradio-wave propagation characteristic estimation technique, employing aray tracing technique.
 7. A base-station cell design method in a mobilecommunication system, wherein a service area, and a traffic densitydistribution within this service area are given to locate base stationswithin the above service area, said base-station cell design methodcharacterized in including a base-station layout decision step ofsequentially deciding until traffic coverage ratio exceeds desiredtraffic coverage ratio and said traffic coverage ratio is defined as arate of a total traffic quantity absorbed by the base stations to allthe traffic quantity that occurs within said service area.
 8. Thebase-station cell design method according to claim 7, said base-stationcell design method characterized in that said base-station layoutdecision step comprises: a step of calculating a traffic absorptionquantity and (or) a communication quality value in each of candidatelocations of said base station; an objective-function calculation stepof calculating a predetermined objective-function responding to thequantity and (or) the value that are this calculated result; and a stepof selecting a layout at which the base station is installed respondingto this objective-function. 9-39. (canceled)
 40. A base-station celldesign apparatus adapted so that, in designing a base-stationinstallment in a mobile communication system, a plurality ofbase-station candidate locations are given within a service area todecide anyone of these base-station candidate locations as abase-station installment layout while a radio-wave propagationcharacteristic estimation technique is used, said base-station celldesign apparatus characterized in including the means for: as aradio-wave propagation characteristic estimation technique within saidservice area with each of said base-station candidate locations taken asa transmission point, using a first radio-wave propagationcharacteristic estimation technique having a first precision to installsaid base station; and as a radio-wave propagation characteristicestimation technique within said service area with a base-stationinstallment location after a case where said base station was installedtaken as a transmission point, using a second radio-wave propagationcharacteristic estimation technique having a precision higher than saidfirst precision.
 41. A base-station cell design apparatus in a mobilecommunication system, wherein a service area, and a traffic densitydistribution within this service area are given to arrange a basestation within the above service area, said base-station cell designapparatus characterized in including base-station layout decision meansfor, with a rate of a total traffic quantity that can be absorbed by thebase station arranged within said service area to all the trafficquantity that occurs within said service area taken as a trafficcoverage ratio, sequentially deciding layouts at which the base stationis installed until said traffic coverage ratio exceeds a desired trafficcoverage ratio.
 42. The base-station cell design apparatus according toclaim 41, said base-station cell design apparatus characterized infurther including deletion base-station decision means for sequentiallydeleting said base stations for which installment was decided until saidtraffic coverage ratio satisfies a desired traffic coverage ratio.
 43. Acomputer-readable program for causing a computer to execute abase-station cell design method adapted so that, in designing abase-station installment in a mobile communication system, a pluralityof base-station candidate locations are given within a service area toinstall a base station in anyone of these base-station candidatelocations, said program characterized in comprising: anobjective-function calculation step of calculating a predeterminedobjective-function responding to a traffic absorption quantity and (or)a communication quality value in each of said base-station candidatelocations; and a base-station layout decision step for deciding a layoutat which the base station is installed responding to thisobjective-function.
 44. The program according to claim 43, said programcharacterized in being adapted so that: in said objective-functioncalculation step, the higher said quantity and (or) value are, thehigher objective-function is given; and in said base-station layoutdecision step, the location of which said objective-function is highestis decided. 45-47. (canceled)
 48. A computer-readable program forcausing a computer to execute a base-station cell design method in amobile communication system, wherein a service area, and a trafficdensity distribution within this service area are given to arrange abase station within the above service area, said program characterizedin including a base-station layout decision step of, with a rate of atotal traffic quantity that can be absorbed by the base stationsarranged within said service area to all traffic quantity that occurswithin said service area taken as a traffic coverage ratio, sequentiallydeciding layouts at which the base station is installed until saidtraffic coverage ratio exceeds a desired traffic coverage ratio.
 49. Theprogram according to claim 48, said program characterized in that saidbase-station layout decision step including: a step of calculating atraffic absorption quantity and (or) a communication quality value ineach of said base-station candidate locations; an objective-functioncalculation step of calculating a predetermined objective-functionresponding to the quantity and (or) the value that are this calculatedresult; and a step of selecting the layout at which the base station isinstalled responding to this objective-function. 50-79. (canceled)
 80. Abase-station design method in a mobile communication system, saidbase-station design method characterized in including: a step of givinga plurality of base-station candidate locations within a service area;and an objective-function calculation step of, with a predeterminedobjective-function, calculating at least one of a traffic absorptionquantity and a communication quality value in a case where a basestation was installed in anyone of said base-station candidatelocations.
 81. A base-station cell design method in a mobilecommunication system, said base-station cell design method characterizedin including: a base-station candidate location setting step of giving aplurality of base-station candidate locations within a service area; anobjective-function calculation step of, with a predeterminedobjective-function, calculating at least one of a traffic absorptionquantity and a communication quality value in a case where a basestation was installed in each of said base-station candidate locations;and a step of employing a result of the objective-function calculated insaid objective-function calculation step to decide a base-stationinstallment location within said service area.
 82. A base-station celldesign method of, in designing a base-station installment in a mobilecommunication system, designing parameters to be set for base stationsgiven in plural within a service area, said base-station cell designmethod characterized in including: an objective-function calculationstep of calculating a predetermined objective-function responding to atraffic absorption quantity and (or) a communication quality value ineach of said base stations; and a base-station parameter decision stepof deciding parameters for installing the base station responding tothis objective-function.
 83. A base-station cell design apparatus for,in designing a base-station installment in a mobile communicationsystem, designing parameters to be set for base station given in pluralwithin a service area, said base-station cell design apparatuscharacterized in including: objective-function calculation means forcalculating a predetermined objective-function responding to a trafficabsorption quantity and (or) a communication quality value in each ofsaid base stations; and base-station parameter decision means fordeciding parameters for installing the base station responding to thisobjective-function.
 84. A computer-readable program for causing acomputer to execute a base-station cell design method of, in designing abase-station installment in a mobile communication system, designingparameters to be set for base station given in plural within a servicearea, said program characterized in including: an objective-functioncalculation step of calculating a predetermined objective-functionresponding to a traffic absorption quantity and (or) a communicationquality value in each of said base stations; and a base-stationparameter decision step of deciding parameters for installing the basestation responding to this objective-function.